There are many types of communications protocols known in the art. One such communications protocol (CP) is MODBUS. MODBUS is a serial communications protocol first published in 1979 for use with its programmable logic controllers (PLCs). It has become a de facto standard communications protocol in industry, and is now the most commonly available means of connecting industrial electronic devices. More particularly, the MODBUS protocol is often used for sending information between a client and server of a MODBUS enabled system. There are many types of CP (e.g., MODBUS) enabled systems known in the art, such as MODBUS and MODBUS TCP/IP enabled systems. An exemplary CP (e.g., MODBUS) enabled system 100 is shown in FIG. 1A. It should be noted that the term “TCP” as used herein refers to transmission control protocols. TCPs are well known to those having ordinary skill in the art, and therefore will not be described herein. The term “IP” as used herein refers to internet protocols. IPs are well known to those having ordinary skill in the art, and therefore will not be described herein.
System 100 is configured for controlling industrial equipment and processes. The system 100 is typically comprised of a first industrial control system (FICS) 102, a gateway node 120, a second industrial control system (SICS) 122, and industrial equipment 118, 126. The FICS and SICS 102, 122 can have a distributed network configuration, i.e., there are application specific modules connected to each other, industrial equipment 118, 126, and operator interfaces via a local control network. The gateway node 120 is configured to enable communications between the FICS and SICS 102, 122.
As shown in FIG. 1A, the FICS 102 generally includes a serial bus 104 and MODBUS server devices 106, 108, 110, 112 connected to and accessible by other portions of the system 100 through the serial bus 104. Each of the MODBUS server devices 106, 108, 110, 112 is comprised of a memory device 130, 132, 134, 136 including respective storage locations 1401, . . . , 140N, 1421, . . . , 142N, 1441, . . . , 144N, 1461, . . . , 146N. Each ofthe memory devices 130, 132, 134, 136 has process parameter information stored therein. Such process parameter information generally includes, but is not limited to, information defining temperature parameters, timing parameters, and liquid level parameters.
SICS 122 is comprised of a computing system (or MODBUS client device) 124. The computing system 124 is typically a general purpose computer processing device. The computing system 124 is configured to allow users to monitor and/or control an industrial process or equipment 126. More particularly, the computing system 124 is configured to enable a user to write parameter information to and/or read parameter information from each of the MODBUS server devices 106, 108, 110, 112.
As known in the art, reading or writing operations within system 100 are interrupted when the gateway node 120 or any MODBUS server device 106, . . . , 112 is found to be unresponsive or operating improperly (or malfunctioning). As should be understood, a MODBUS server device 106, . . . , 112 is unresponsive when it does not return a message in response to a write request or reading query. A MODBUS server device 106, . . . , 112 can operate improperly (or malfunction) when its internal hardware or software fails. The interruption occurs during a time out process. A typical time out process performed by the computing system 124 is shown in FIG. 1B. Similarly, a typical time out process performed by the gateway node 120 is shown in FIG. 1C. As shown in FIGS. 1B-1C, the interruption period is defined as a “time out period.” The phrase “time out period” as used herein refers to a predetermined period of time that is fixed in the software to be long enough for a gateway node 120 or any MODBUS server device 106, . . . , 112 to respond normally, i.e., return a response message to the computing device 124 or the gateway node 120, respectively.
Despite certain advantages of system 100, it suffers from certain drawbacks. For example, write/read processes are restricted to a single write or read request at any given time. In addition, an unresponsive or malfunctioning MODBUS server device (e.g., server device 108) adversely affects the system communications with the other MODBUS server devices (e.g. devices 106, 110, 112). In this regard, no other write request or read query can be made to this MODBUS server device (e.g., device 108) or other MODBUS server devices (e.g. devices 106, 110, 112) during a time out process. Since no data is transferred during time out periods, the rate of data transfer in system 100 is reduced by time out periods. As such, there is a need for an improved CP enabled system capable of reducing the impact of an unresponsive or malfunctioning CP (e.g., MODBUS) enabled device on system communications.